In recent years, electronic devices having a display panel provided with a touch panel function are developed as a user interface, such as a cellular phone, a Personal Digital Assistant (PAD), and a personal computer. In the electronic devices equipped with the touch panel function, it is studied to provide the touch panel function by attaching a touch panel substrate independently produced from the display panels, such as a liquid crystal display panel and an organic electroluminescence display panel.
Moreover, in a display device having scanning lines and signal lines, a technology of manufacturing the display device with sensor elements is researched.
Moreover, as a sensing system for reading images, a technology, i.e., a capacitance sensor system is studied to detect a contact position on the surface of the display panel by a fingertip or a nib, in which a detection electrode is provided in place of an electrical optical sensor element, and an information of the contact position is detected by a capacitance change between the electrode and the finger, etc.
In the display device using a capacitance sensor system, an in-cell technology, in which the sensing function is incorporated into the display panels such as the liquid crystal display panel, is developed briskly. By the way, when the touch panel function is realized by building a sensing circuit in the substrate forming the display panel for detecting a contact position on the substrate which constitutes the display panel, degradation of the display grace may occur because both the display function and the sensing function share a portion of circuits thereof.
For example, in the display device with an input function provided with the sensing circuit and the display circuit, some signal lines arranged in a vertical direction are shared in the sensing circuit and the display circuit, and a reading operation of the sensing circuit and the display operation are performed by time sharing. Therefore, at a time between after the reading operation of the sensing circuit and right before the starting of the display operation, the signal for the reading operation of the sensing circuit is written in the signal line. Since this state differs from that of the signal line in the case of repeating the usual display operation, the display immediately after the sensing operation is affected, and display grace deteriorates.